A conventional turn signal lamp assembly having a structure in which a front surface of a light-guiding member (a surface of a light-guiding member, the surface facing outward when the turn signal lamp assembly is assembled to a vehicle door mirror) is covered by a transparent member is described in Patent Literature 1 indicated below. As illustrated in FIG. 7, the turn signal lamp assembly is configured in such a manner that an outer lens 5 (transparent member) on the front side (side facing outward when the turn signal lamp assembly is assembled to a vehicle door mirror) and a base housing 3 (non-transparent member) on the back side (side hidden from the outside when the turn signal lamp assembly is assembled to a vehicle door mirror) form a casing (enclosure) and an inner housing 4 is incorporated in an internal space surrounded by the casing. The inner housing 4 includes an inner member (non-transparent member) and a light-guiding member 6 (transparent member), the light-guiding member 6 is incorporated into the inner member from the front side of the inner member, and the inner housing 4 is held by the base housing 3. In the inner housing 4, a light source unit 8 including LEDs 9, 10 and 11 is incorporated. Since the light-guiding member 6 is covered by the outer lens 5, the light-guiding member 6 is prevented from being damaged as a result of being hit by a stone or the like, and the light-guiding member 6 is also prevented from its light-guiding function being impaired as a result of rain drops adhering to the light-guiding member 6.